The present invention relates to a two-for-one twisting spindle in which a thread is threaded by compressed air.
In a two-for-one twisting spindle the thread is usually removed in an upward direction from a stationary supply spool, is then introduced into the upper end of the thread inlet tube, is guided in a downward direction and thereby fed from the thread guiding tube through the spindle rotor where it exits in a radial direction from the thread guiding channel, respectively, thread outlet channel of the thread storage disk. From this outlet channel, the thread is guided in an upward direction by a balloon rotating about the supply spool. A thread guiding member or a thread guiding eye is commonly the upper limitation of the thread balloon. The thread is then guided via a leading spool to a reciprocating thread guide and from there to a winding spool which in general is driven by a friction roller.
For threading a thread through a spindle, compressed air actuated threading devices are known which are provided in the area of the hollow spindle axle. These threading devices suck the thread into the hollow spindle axle by a suction effect (injector effect) and convey the thread through the thread guiding channel of the thread storage disk with the aid of the jet of compressed air.
In order to operate the threading device it is required that the injector nozzle is provided with compressed air which is fed to the injector nozzle via respective compressed air channels. It is known from the German patent 24 61 796 to guide the compressed air through stationary spindle parts such that the compressed air channel is a component of the stationary spool pot and is guided from the outer circumference of the pot to the injector nozzle. In this embodiment, the compressed air channel has a segment that extends radially through the bottom of the spool part and communicates with a further segment extending through the hollow hub of the spool pot. According to German patents 20 35 025 and 30 12 427 it is also known to arrange the injector nozzle centrally within the thread storage disk whereby the compressed air line, respectively, the compressed air channel is guided centrally through the whorl. In such an embodiment a coupling segment is required in the area of the compressed air line between a stationary and a rotating part.
In a two-for-one twisting spindle of the aforementioned kind the pneumatic threading of a thread through the hollow spindle axle and the thread storage disk requires a free thread passage within the area of a thread brake which is needed for stabilizing the twisting process. This is achieved, for example, when the braking cartridge of a cartridge brake is released from the two braking rings on which the braking cartridge is supported so that both passages through the braking rings are opened.
An arrangement corresponding to the above described embodiment is disclosed in the German patent 28 30 265 (FIGS. 6 and 7). For the given constructive dimensions of a respective thread brake the suction, respectively, vacuum forces generated by the suction effect (injector effect) are relatively small so that the piston, which encloses one of the braking rings and which is displaced by the vacuum forces for releasing the braking cartridge, may be supported at the cylinder walls only with minimal friction forces. In practice, the return elements for returning the piston must be adjusted exactly to the corresponding displacement forces, respectively, the spring force of the cartridge. However, the vacuum forces which may be reached by the injector effect are limited. The return force acting on the piston with the lower braking ring must be great with respect to the cartridge force.
It is therefore an object of the present invention to provide a two-for-one twisting spindle of the aforementioned kind in which the vacuum generated by the suction effect (injector effect) is sufficient to open and close the thread brake in a reliable manner.